In gas-cooled high temperature nuclear reactors, the primary coolant (particularly helium) after traversing the reactor core may contain fission fragments which tend to deposit in the portions of the coolant circulation path adjacent the outlet of the reactor, complicating maintenance and repair because of the high level of radioactivity resulting from such fission product deposits.
When the path also includes a helium turbine, for example, the problem of maintenance and repair is pronounced and indeed may be impossible if the turbine is permitted to be contaminated by such fission products which invariably enter the coolant gas stream.
It has thus been proposed (see German patent documents-open applications-DE-OS No. 26 55 296 and DE-OS No. 26 55 310) to provide in the coolant path a filter which operates by exchange principles to trap atomic and molecular particles of the fission products and thereby remove them from the coolant gas.
Such filters include metal walls which define flow passages for the coolant and upon which the fission products are collected.
As a consequence, any dust particles within the coolant gas do not become contaminated with the fission products and the residual radioactivity of the gas and its components, downstream of the filter, can be reduced or eliminated. These publications also deal with the mathematical, dimensional and optimization factors for such filters in addition to describing metal walls which are effective to collect the fission products.
While these filters theoretically appear to be capable of effective use in the manner described, they are not technologically practical because of high fabrication cost and poor geometric efficiency.